The invention relates to a tire chain with junction points, each formed by at least three vertical links standing upright, that is to say oriented perpendicularly to the tire surface, and by one horizontal link lying flat, that is to say oriented parallel to the tire surface, the horizontal link of at least one junction point having the form of a shackle with an essentially annular main part and with two outward-directed ends arranged at a distance from one another and bridged by a connection part.
A chain netting for a tire chain of the above type is known from German Offenlegungsschrift No. 2,658,009 corresponding to U.S. Pat. No. 4,147,023. In the known chain netting, at least one junction point has a horizontal link which is designed as a chain joint and in the annular main part of which the vertical links can be inserted through an insertion slot subsequently closed by means of a screw bolt which connects to one another the outward-directed ends of a shackle also forming the main part, these ends having aligned bores for receiving the screw bolt. The advantage of a junction point of the above type is that, before assembly, its horizontal link can be subjected to heat treatment resulting in a sufficiently high surface hardness. There is no need to spread open the shackle or subsequently press it shut respectively before and after the vertical links have been hooked in, particularly because the position of the ends of the shackle does not need to be changed during or after the links have been joined together. However, the advantage described entails the disadvantage that it is not possible with sufficient reliability to prevent the connecting element from loosening under unfavourable loads. In addition, the production outlay for the chain joint described is comparatively high.
The danger of unintentional opening, inherent in a chain joint, disappears when the horizontal link of a junction point is closed by means of welding after the vertical links have been hooked in. Tire chains having junction points formed in a corresponding way are sufficiently known. In these, the end faces of a bent structural-bar section forming the horizontal link of a particular junction point are joined directly to one another by means of resistance butt welding. However, as already mentioned above, such a design of a junction point prevents the possibility of heat treatment resulting in a sufficiently high surface hardness of the horizontal link, before the links are assembled, since, in order to hang the vertical links in the horizontal link, it is necessary to spread open the horizontal link beforehand and/or bend it together subsequently, and at the same time a surface-hardened shackle is particularly inclined to form hairline cracks. In practice therefore, in such cases joint heat treatment of all the links is also carried out after the particular horizontal link has been welded shut. However, even this entails disadvantages in that, on the one hand, the choice of different materials for the horizontal and vertical links is limited and, on the other hand, the technical devices for the heat treatment of a chain netting are more expensive than those for the heat treatment of individual chain links. Because of the above-indicated difficulties of welded constructions, they have not found general acceptance despite the advantage that there is no fear that their junction points will loosen unintentionally.